Discrete high molecular weight triarylamine dendrimers prepared by palladium-catalyzed amination
Discrete high molecular weight triarylamine dendrimers prepared by palladium-catalyzed amination
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DOI：
10.1021/ja972806d
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发表时间：
1997-12-03
影响因子：
15
通讯作者：
Fry, AJ
中科院分区：
文献类型：
--
作者：
Louie, J;Hartwig, JF;Fry, AJ
三芳基胺是一类重要的化合物，因为它们形成稳定的铵自由基阳离子。因此，三芳基胺可以是已显示铁磁耦合的高自旋多自由基的结构单元，1，2以及导电聚合物。也许最常见的是，三芳基胺已被用作电致发光器件中的空穴传输层。4-7稳定的自由基阳离子也可以引发周环反应，8作为电催化剂，9，10或作为温和的选择性氧化剂。芳胺大分子的合成受到铜介导的Ullmann化学的适度产率的限制，但是最近我们的小组和Buchwald的小组出现了新的钯催化的形成芳胺的方法。18-21我们报道了首次使用这种钯催化的化学反应来形成纯的离散芳胺低聚物和最大的离散芳胺树枝状聚合物。形成三芳基胺的三种新的钯催化反应示于方案1中。二甲苯基氨基锂和4-溴甲苯在1mol%Pd [P（邻甲苯基）3] 2（1）存在下在甲苯中于90 ℃反应1小时后定量产生三甲苯基胺。或者，二甲苯基胺和4-溴甲苯在化学计量的叔丁醇钠和1摩尔% Pd [P（邻甲苯基）3] 2的存在下反应，以92%的产率得到三甲苯基胺。对于后一反应，在90 ℃下获得1小时的定性半衰期。我们以前已经表明，苯胺与芳基溴在催化量的前体Pd（DPPF）Cl 2（DPPF）二苯基膦基二茂铁）的存在下反应，以高产率得到二芳基胺。15，19我们在这里表明，DPPF-连接的钯可以产生二芳基胺或三芳基胺。Pd（DBA）2（DBA）二亚苄基丙酮）和DPPF（2.5mol%）的组合催化在2.1当量叔丁醇钠存在下由4-甲苯胺和2.1当量4-溴甲苯以89%产率形成三甲苯基胺。对于这项工作最重要的是，这些反应表明，我们可以使用这种化学方法以高产率生产电子感兴趣的三芳基胺树枝状聚合物，而这些树枝状聚合物以前是以中等产率制备的。在2mol%催化剂1的存在下，由三（4-溴苯基）胺和3.3当量的二苯氨基锂制备第一代树枝状聚合物4，4′，4 ″-三（N，N-二苯氨基）三苯胺（TDATA，2）（方案2），分离产率为84%。该分子通过铜化学以仅22%的产率制备。22 Ullmann化学的低产率阻碍了更高代三芳基胺树枝状聚合物的制备。我们在这里证明，钯化学可以产生更大的超支化芳胺。采用收敛策略23，我们制备了最大的三芳基胺星状树枝状聚合物，如方案3顶部所示。N，N-双（4-溴苯基）苯甲胺24（3）和2.2当量的二甲苯基氨基锂在2mol%1存在下在甲苯中反应，通过沉淀和从THF：EtOH（1：1）中重结晶，以95%的分离产率得到苄基保护的4。在通过沉淀和从THF：EtOH（1：1）中重结晶纯化后，用50 psi H2经Pd/C将4脱苄基，得到胺5，产率为88%。由5的锂化产生的氨基锂6与0.3当量的三（4-溴苯基）胺在3.5摩尔% 1的存在下反应，得到第二代树枝状聚合物7。Starburst 7可溶于苯、甲苯和四氢呋喃，并通过从THF：EtOH中重结晶以80%产率分离。通过1H和13 C NMR光谱判断该物质是纯的。硅胶色谱法得到分析纯的物质，产率为64%。总产量…
Triarylamines are an important class of compounds because they form stable aminium radical cations. Thus, triarylamines can be building blocks for high-spin polyradicals that have shown ferromagnetic coupling, 1, 2 as well as for conductive polymers. 3 Perhaps most commonly, triarylamines have been used as the hole-transport layer in electroluminescent devices. 4-7 Stable radical cations can also initiate pericylic reactions, 8 act as electrocatalysts, 9, 10 or act as mild and selective oxidizing agents. 11 The synthesis of arylamine macromolecules12 has been limited by the modest yields of the copper-mediated Ullmann chemistry, but new palladium-catalyzed methods to form arylamines have emerged recently from our group13-17 and Buchwald’s group. 18-21 We report the first use of this palladium-catalyzed chemistry to form pure discrete arylamine oligomers and the largest discrete arylamine dendrimer. Three new palladium-catalyzed reactions that form triarylamines are shown in Scheme 1. Lithium ditolylamide and 4-bromotoluene reacted in the presence of 1 mol% Pd [P (o-tolyl) 3] 2 (1) in toluene to produce tritolylamine quantitatively after 1 h at 90 C. Alternatively, ditolylamine and 4-bromotoluene reacted in the presence of stoichiometric amounts of sodium tert-butoxide and 1 mol% Pd [P (o-tolyl) 3] 2 to give tritolylamine in 92% yield. A qualitative half-life of 1 h at 90 C was obtained for the latter reaction. We have previously shown that anilines react with aryl bromides in the presence of catalytic amounts of precursor Pd (DPPF) Cl2 (DPPF) diphenylphosphinoferrocene) to give diarylamines in high yields. 15, 19 We show here that DPPF-ligated palladium can produce diarylamines or triarylamines. A combination of Pd (DBA) 2 (DBA) dibenzylideneacetone) and DPPF (2.5 mol%) catalyzed the formation of tritolylamine in 89% yield from 4-toluidine and 2.1 equiv of 4-bromotoluene in the presence of 2.1 equiv of sodium tert-butoxide. Most important for this work, these reactions suggested that we could use this chemistry to produce electronically interesting triarylamine dendrimers in high yields that were previously prepared in modest yields. The first generation dendrimer 4, 4′, 4′′-tris (N, N-diphenylamino) triphenylamine (TDATA, 2) was prepared from tris (4-bromophenyl) amine and 3.3 equiv of lithium diphenylamide in the presence of 2 mol% catalyst 1 (Scheme 2) in 84% isolated yield. This molecule was prepared in only 22% yield by copper chemistry. 22 Low yields from Ullmann chemistry have prevented the preparation of higher generation triarylamine dendrimers. We demonstrate here that the palladium chemistry can produce larger hyperbranched arylamines. Employing a convergent strategy23 we prepared the largest triarylamine starburst dendrimer, as shown at the top of Scheme 3. Reaction of N, N-bis (4-bromophenyl) benzenemethanamine24 (3) and 2.2 equiv of lithium ditolylamide in the presence of 2 mol% 1 in toluene gave benzyl-protected 4 in 95% isolated yield by precipitation and recrystallization from THF: EtOH (1: 1). Debenzylation of 4 with 50 psi of H2 over Pd/C gave amine 5 in 88% yield after purification by precipitation and recrystallization from THF: EtOH (1: 1). Reaction of lithium amide 6, generated from lithiation of 5, and 0.3 equiv of tris (4-bromophenyl) amine in the presence of 3.5 mol% 1 gave second generation dendrimer 7. Starburst 7 is soluble in benzene, toluene, and tetrahydrofuran and was isolated in 80% yield by recrystallization from THF: EtOH. This material was judged pure by both 1H and 13C NMR spectroscopy. Silica gel chromatography gave analytically pure material in 64% yield. The overall yield …